Many applications exist in industry where it is desirable to control the behavior of a system or plant having a variety of different components. Examples of such components include machine tools, robotics, environmental systems and chemical processes. A typical controller would contain or be provided with a description of the desired behavior of the plant, be able to measure the condition(s) or state(s) of the plant, compare that state against the desired behavior and then direct the plant closer to the desired behavior by adjusting inputs to the plant. Such a system is referred to as a feedback control system.
In general the plant will have multiple inputs and multiple output states. Typically, the plant inputs are drive signals to actuators which are capable of affecting the plant's states, and the plant's outputs are signals from transducers which measure plant states.
Commonly the controller is a monolithic device. Its function is to: convert the signals representing the plant states into a form suitable for computation; obtain from an external source or from internal memory the desired plant behavior; compare the desired behavior with the actual behavior as represented by the obtained plant states; compute the appropriate way to direct the plants actuators; and output the required signals to the plant's actuators.
One modification to a typical monolithic controller structure splits the parts of the controller which convert the signals representing the plant states and/or drive the plant inputs out into one or multiple units. These units are then connected to the main control unit using some form of digital network.
Often the plant state signals and plant inputs are analog in nature which can be converted to digital signals. There are advantages of signal quality and reliability in performing a conversion to and from digital format in close proximity to the plant. Additionally, transmitting the resulting digital data across a shared digital network can reduce wiring complexity. In some plants, modules are added to the plant to make its inputs and outputs appear digital to the controller and allow the transmission of this data over a digital network. The resulting digital network can take many forms including, for example, a ring, tree, star or a combination of such topologies.
In any event, the control calculations are still performed in a central location called the controller and the description of the network connections and the data to be transmitted are located at this central location. Typically, the controller is referred to as the master and the nodes with which it communicates across the network are called slaves. In such environments, the controller or master manages the flow of data to, from and between the various slave devices.
The present invention is an improvement on such prior systems and processes.